Epic story-driven FPS running on the Build Engine

Dhewm 3 is a Doom 3 GPL source port

EDuke32 is an awesome, free homebrew game engine

Fast arcade first person shooter

The Free and Fast Arena Shooter

Source port for Build engine games

Free agile arena shooter

First-person shooter game

Top-down shooter action RPG

Open Source voxel shooter

Aliens vs Humans, First Person Shooter game with elements of Real Time Strategy

A modernization effort of DOOM-3-BFG

Classic arena first person shooter

Yamagi Quake II is an alternative client for id Software's Quake II

Leading the way in newschool multiplayer Doom online

A Doom II mod with weapons and mechanics inspired by Quake Champions

Tank digging battle game

Open Source voxel shooter

A Quake mod based on the retro shooter SPRAWL

The orb ponderer's arena first-person shooter

FPS aim trainer

A Zandronum 3.0 fork with improved netcode, configurable movement and many small tweaks

Fast paced, first person strategy game

Free fast paced arena shooter

Modern cross-platform port of the Descent engine

ReC98 source port of the first Seihou Project game

Game engine for Classic Doom

a modern QuakeWorld client focused on competitive online play

Open source first person shooter

Open source first person shooter